The present invention relates to abrasive grit structures used in the grinding and shaping of various materials.
Abrasive grit tool structures such as grinding wheels and the like conventionally have an outer grit particle surface which is used to remove pieces of a workpiece for shaping and finishing a workpiece. In prior structures abrasive grits have been attached to tool surfaces by placing a single layer of grit particles on a tool form and then bonding the grits to the tool by using a brazing metal or by an electroplating coating which grips the grit particles. These structures along with other types of structures have the disadvantage in that the resulting tool may have grits of widely varying heights, erratic grit edges, flat spots or other irregular surfaces which tend to present an uneven grinding surface to the workpiece. In grinding structures the desired effect is to present the abrasive grits to the workpiece at an even level in order to most effectively shape the workpiece. Thus, many of the prior structures have failed to meet this goal.
The electroplated structures have generally used a nickel metal for the electroplating of the metal substrate in order to hold the grit. The electroplated layer used in these structures generally had to be of a depth such that the metal would build up on the sides of the grits (i.e. the formation of a meniscus) in order to provide a mechanical grip around the grit particles. This mechanical grip was required because there was generally little or no chemical binding or alloying between the grit particles, particularly diamonds, and the metal material.
Brazing materials such as nickel-chromium alloys which form chromium carbide bonds with diamond particles were also used. Because the stresses and strains imposed on such a structure (particularly when the diamond particles are close to or in contact with a steel substrate) tended to break the chromium carbide bond during cooling, it has generally been required in the past to have such a mechanical gripping bond even when using these types of alloys.
Other grinding wheel structures have been produced by either pressure forming a grinding wheel in a mold, or grinding surfaces have been added to tools by placing the individual tool in a mold and using pressure molding and brazing procedures to attach the grinding surface to a substrate mold surface. As is readily appreciated such procedures are costly, time consuming and require special equipment.
Additionally, some structures of the past have commonly not provided adequate space between the grinding particles. This results in a diminished useful lifetime of the tool due to particles of the workpiece being lodged between the grit particles or extending over the grit particles such that contact between the individual grit particles and the workpiece is reduced, thereby inhibiting the grinding action.
Diamonds have long been used and are preferred in the art as a grinding grit particle. Because of the nature of diamonds it is hard to create a structure whereby a diamond can be held or bonded to a surface in such a manner that it will not break off during the grinding process. Therefore, it has been a problem in grinding wheels using diamond grits that while initially the diamond grinding wheel worked relatively well, after a period of use the diamond grit particles would eventually break away from the substrate structure. This would reduce the number of actual cutting grit particles which were available to shape or form the workpiece thereby foreshortening the useful life of the tool.
According to the present invention there is provided an abrasive grit structure which may be selectively and securely attached to a substrate tool structure without the use of high pressure or other complex manufacturing methods as was sometimes necessary in the prior art. Thus, with the present invention a grinding tool can be produced at a reduced cost.
The present invention also has the advantage of allowing for efficient use of the grit structure by placing the grit particles in a homogeneous and level pattern wherein each of the grits are configured at substantially the same plane in the final tool surface. The structure of the present invention provides a final grit structure whereby it is substantially ensured that each grit will contact and effectively cut the surface to be ground.
The present invention also allows space between the grit structures which inhibits clogging between the structures whereby the grinding tool life will be extended. The present invention also has the advantage that the diamond or other hard grit like constituent is securely held by the surrounding structure such that it will have a greater bonded life expectancy than such structures produced in the past.
According to the present invention, there is provided a bonded abrasive grit structure which is selectively attachable to a tool surface. The structure includes a plurality of peaked portions on a substrate layer with the peaked portions each having an apex and a base portion. Each of the peaked portions has at least one abrasive grit particle at the apex or others near the apex. The abrasive grit particle is substantially surrounded in the apex by a setting material. The remainder of the structure comprises a particulate matter having a melting point temperature higher than a predetermined temperature (higher than a melting point of a brazing compound to be used in the present invention). A flexible hydrocarbon resin binder is dispersed throughout the structure for temporarily binding together the abrasive grit particles, the setting material and the particulate matter. The hydrocarbon resin binder is volatizable and drivable from the structure at a first relatively low predetermined temperature. The structure is brazable to a tool surface by the infiltration of a brazing material therethrough and onto the tool surface at a second higher temperature which is lower than the melting point of the particulate material.
Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following description when considered in connection with the accompanying drawings.